AH-27
Typical LDO Regulator
V
IN
C
IN
22µF
IN
V
REF
GND
ADJ
EN
MIC29152
V
CONTROL
C1
0.1µF
R
T
33k
R3
240k
D1
1N4148
R2
100k
OUT
V
ADJ
R1
300k
C
OUT
22µF
V
OUT
Micrel
R4
240k
C
T
10µF
D2
1N4001
Figure 5. Slow Turn-On Without Pedestal Voltage
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
10
5
0
4
2
0
0
0.2
0.4
0.6
0.8
1.0
TIME (s)
Figure 6. Turn-On Behavior of Figure 5
which corresponds to the first 60% of the capacitor RC charge
curve. R3 is calculated as follows:
at turn-on time force
V
ADJ
= 1.5V
(just slightly higher than V
REF
)
then
I
CONTROL
=
1
.
5V
R1
×
R2
R1
+
R2
Since the MIC29152 is a low-dropout regulator, 6V was
chosen for V
IN
(min). This corresponds to the small (approxi-
mately 40 msec) delay before the output begins to rise. With
7V input the initial delay is considerably more noticeable.
and
R3 =
V
IN min
−
0.6V
I
CONTROL
3-204
1997
MICREL [ MICREL SEMICONDUCTOR ]
